Automatic ringing system.



A H. WEISS.

AUTOMATIC RINGING SYSTEM. APPLICATION FILED AUG. 17, 1910.

1,030,038. Patented June 18, 1912.

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A PLIOATION FILED AUG 17 1910 June 18,

2 SEBETSSHEET 2.

R IIHIHIIIIIMHIII- COLUMBIA PLANDORAPH CO-IWASHINOTON. D. C.

UNTTED 8TATE PATEN T OFFTE ALFRED H. WEISS, OF WIL'METTE, ILLINOIS,ASSIGNORTO KELLOGG SWITGI-IBOARD AND SUPPLY COMPANY, OF CHICAGO,ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC BINGING SYSTEM.

To all whom it may concern Be it known that I, ALFRED H. WEISS, acitizen of the United States, residing in Wilmette, county of Cook, andState of Illinois, have invented certain new and useful Improvements inAutomatic Ringing Systems, of which the following is a specification.

My invention relates to common battery telephone exchange systems, andhas for its object the provision of a simplified and efficient signalingarrangement for such systems. The arrangement is adapted particularlyfor signaling upon telephone party lines, although not limited to suchuse.

In the drawings, Figure 1 is a telephone system embodying one form of myinvention, and Fig. 2 shows my invention adapted for use with a trunkcircuit for making connection between subscribers whose lines terminateat different central oiiices.

Referring to Fig. 1, two subscribers lines A and B are shown terminatingat the central oflice C. The line A is shown as an individual line; thatis, having a single subscriber, and line B is a polystation line havingfour subscribers. Any form of common battery substation circuit may beused, but, for the purpose of illustration I have shown a well-knownsubscribers circuit in which the bell 1 is normally bridged across theline in series with a condenser 2 for signaling purposes. lVhen thereceiver is removed :Erom the switch-hook for conversation, this pathfor ringing current is broken at the switch-hook contacts and a path fortalking and for energizing the substation transmitter 3 is established.This latter circuit includes the transmitter and impedance coil 4 inseries for the energizing battery current, the voice currents flowingthrough the receiver 5 and condenser 2 which are placed in a shuntcircuit around the impedance coil 4- Assuming the subscriber of the lineA desires connection with one of the subscribers on line B, thetelephone receiver would be removed from its switch-hook closing a pathfor current from the central oflice battery 6, through the line relay 7,the limbs of the telephone line to the ground pole of battery at 8.Responsive to this current, the line relay will attract its armaturelighting the line lamp 9. Upon seeing the line lamp lighted, theoperator will insert the answering plug 10 of Specification of LettersPatent.

Patented June 18, 1912.

Application filed August 17, 1910. Serial No. 577,664.

the cord circuit in the jack 11 of the calling llne. Current will thenflow from the battery 12 through the sleeve supervisory relay 13, sleevestrand of the cord circuit, sleeve contact of the jack and through thecut-oil relay 14k to battery, energizing the cutolt relay, which willattract its armatures 15 and 16. The attraction of armature spring 15will open the circuit of the line relay '7 retiring the line signal 9,and the attraction of the contact spring 16 will remove the ground 8from the line and establish connection between that limb of the line andthe sleeve contact of the jack. Upon the attraction of the contactspring 16, a portion of the current flowing to ground through thecut-off relay 1 1 will flow over the telephone line to energize thesubstation appa ratus and back to the central ofiice, over the otherlimb of the telephone line, through the tip contacts of the jack andplug and through the winding of the tip supervisory relay 17 to battery.

It will be noted that current through the cut-cit relay 14 energized thesleeve supervisory relay 13 to place the supervisory lamp 18 incondition to operate, but the flow of current over the line and throughthe tip supervisory relay 17 operated to open the circuit of thesupervisory lamp 18 at the contacts of the latter relay, so that thelamp 18 remains inert. The supervisory relay 13 is energized over alocal circuit so that the supervisory lamp 18 is placed in condition tolight at the contacts of this relay as long as the plug is inserted inthe jack, while the circuit of the tip supervisory relay17 is throughthe substation apparatus, so that the supervisory lamp 18 is placed incondition to light or remain inoperative, dependent upon the position ofthe receiver at the subscribers station, and the consequent at tractedor unattracted condition of the contacts of supervisory relay 17.

Having noticed the line signal 9 and plugged into the calling line, theoperator throws her listening key 19 bridging her operators telephoneset across the line, and inquires the number desired from the call ingsubscriber. The talking circuit between the operator and the callingsubscriber will be over the limbs of the calling line, the tip andsleeve strands of the answering end of the cord circuit and conductors20 and 21 to the contacts of the listening key between which theoperators telephone is bridged. Ascertaining that a subscriber on theline B is desired, the operator would test the idle or busy condition ofthe line by touching the tip of the calling plug to the sleeve contactof the multiple jack of the desired line. If the line was in use, abattery potential would exist at the sleeve contacts of the jacks, dueto the flow of current through the sleeve supervisory relay 13, sleevecontacts of the plug and jack at the operators position where aconnection was established, with the desired line. The tip of thecalling plug of the operator testing would be connected with groundthrough conductor 22, the back normally closed contact 23 of the callingsleeve supervisory relay 24, conductor 25, normally open contact 26 ofthe ringing key, conductor 27 and impedance coil 28. If the desired linewas idle and no potential existed at the sleeve contact of the multiplejacks of the line, no current would flow through this testing circuitwhen the tip of the plug was touched to the sleeve of the jack, but ifthe line is in use and a battery potential exists at the sleeve of thejack, current will flow through this testing circuit as the tip of theplug is touched to the sleeve of the jack in testing. The kick ordischarge from the impedance coil 28 as the tip of the testing plug istouched to and removed from the sleeve of the jack of the line beingtested, flows through the condenser 29 and the tertiary winding 30 ofthe operators induction coil to ground through battery 6, thus producingan inductive click in the operators telephone receiver, notifying herthat theline desired is busy. If the desired line is idle, the operatorinserts the calling plug of the cord circuit in the jack of the desiredline. This closes a path for current from the battery 6, through thesleeve supervisory relay 24, the sleeve strand of the calling end of thecord circuit, the sleeve contacts of the plug and jack and through thewinding of the cut-off relay 35 to ground. The cut-off relay attractsits contact springs cutting 01f the line relay 36 and the line lamp 3?from the one limb of the called line B and removing the ground 38 fromthe other limb of said line, connecting this latter limb with the sleevecontact of the jack. The energiza tion of the sleeve supervisory relay24 opens back normally closed contact 23 of said relay removing thetesting conductor 25 from the tip contact of the plug and establishingconnection with its alternate nor mally open front contact. The circuitof the supervisory lamp 39 is also completed by the attraction ofcontact spring 40 of the supervisory relay 24, thus placing thesupervisory lamp 39 in condition to operate, and as the tip supervisoryrelay 41 is deenergized due to the fact that the subscribers telephonehas not yet been removed from its hook, the supervisory lamp 39 islighted through battery 6, over conductor 42, closed contact 40, ofsupervisory relay 24, conductor 43, and normally closed contact 44 ofsupervisory relay 41. Then the called subscriber responds, thesupervisory relay 41 will be energized over the telephone line B,attracting its normally closed contact 44 and extinguishing thesupervisory lamp 39 to notify the operator that the subscribers are incommunication.

Any system of signaling to select the subscriber desired may be employedwith my invention, but I prefer to use a well-known selective system inwhich a different frequency of current is used to operate the bell ateach substation, the bell at each substation being adapted to respond toits particu lar frequency and being unresponsive to the frequenciesadapted to ring the bells at the other stations upon the line.

I have indicated four ringing keys, 31, 32, 33 and 34 adapted to sendout current from a suitable source such as the generator 35, to operatethe bell at one of the substations upon the line B. I preferably providea single cont-act 45 adapted to operate with each of the ringing keys31, 32, 33 and 34, the arrangement being such that when any of the keys31, 32, 33 and 34 are completely depressed to connect generator currentwith the line, the contact 45 will be closed momentarily, the ringingkey 31, 32, 33 or 34 remaining closed to keep generator current upon theline, but the key 45 returning to its normally open position afterhaving been closed momentarily by the act of depressing the ringing keysmentioned.

After findingthe line idle as above described, and inserting the callingplug in the jack thereof, we will assume that the op erator throws theringing key 31 to signal the desired subscriber upon the line. As justdescribed, this would close the normally open cont-act 45 temporarily,and the ringing contact 31 permanently, for the purpose of continuouslysignaling the subscriber until he responds to the call. hen the normallyopen contact 45 is closed, current flows from the battery 12 through thecontrol relay 46, the normally open contact 47, of answering sleevesupervisory relay 13, conductor 48, contact 45, conductor 49 andconductor 43 to ground at the normally closed contact 44 of supervisoryrelay 41. Current in this path would energize the control relay 4G andopen the cord circuit at its normally closed contacts 50 and 51 toprevent ringing current from passing back over the line of the callingsubscriber. The energization of the control relay 46 would also closethe locking circuit for said relay through its normally open contact 52which may be traced fro-m the battery 12 through the winding of saidrelay 46, the normally open contact 47 of supervisory relay 13,conductors 53 and 43 tothe ground contact 44. The control relay 46 wouldtherefore remain energized until the ground contact 44 was broken by theenergization of supervisory relay 41, when the called subscriberresponded by removing his telephone receiver from its hook. The contact45 should remain closed long enough to establish this locking circuitfor the control relay 46. The closing of the ringing key contact 45 alsocloses a path for current through the flip-flop relay 54, which may betraced from battery 6, conductor 42, circuit breaker 55, the winding offlip-flop relay 54, conductors 56 and 57, contact 45 and conductors 49and 43 to ground 44. When the contact 45 is open, however, the circuitof the flipfiop relay 54 is continued from point 58, over conductors 48and 53, contact 52 of control relay 46 and conductor 43 to the groundconnection 44. So that the flip-flop relay 54 is first preferablyenergized through the ringing key cont-act 45, and is afterwardenergized through the locking contact 52 of the control relay 46.

The circuit breaker 55 in the circuit of the flip-flop relay 54 and thecircuit breaker 59in the generator circuit, are preferably mounted uponthe same shaft so as to rotate together, and the segments thereof are soproportioned that the live contact of the circuit breaker 55 will be ofslightly longer duration than the live contact upon the circuit breaker59, so that the flip-flop relay will have its circuit closed by thecircuit breaker 55 and be energized to connect generator current withthe line at its contact, just before the circuit breaker 59 is inposition to connect generator current with the line at the ringing keycontacts 31, and the live contact at circuit breaker 59 should bemaintained so as to keep the generator circuit intact at the contacts ofthe flip-flop relay until the generator circuit has been broken by thecircuit breaker 59. That is, the generator circuit should be made at thecontact of the flip-flop relay before it is made by the circuit breaker59, and should be maintained at the contact of the flip-flop relay untilafter it is broken by the circuit breaker 59. If the circuit breaker 55in series with the flip-flop relay should open the circuit of that relayand allow its armature to drop back before the ringing cir cuit wasopened by the circuit breaker 59 in series with the generator, thedischarge from the substation condenser over the tip side of the linewould pass through the tip supervisory relay 41, energizing it andremoving the ground 44, which would open the locking circuit of controlrelay 46, thus restoring the ringing circuit to normal be fore thesubscriber had responded to the an instant after the ringing current hasbeen removed at each revolution of the circuit breaker 59 and until. thedischarge from the condenser at the substation has passed over the pathjust traced to the armature 60 of the flip-flop relay 54, and from thatpoint through conductor 61, contacts 31 of the ringing key and thegrounded segment of circuit breaker 59 to ground. The flip flop relay 54continues to intermittently close its contacts 60 in response to therevolutions of the circuit breaker 55- to put ringing current upon theline at that point, and the circuit breaker 59 rotating synchronouslytherewith continues to intermittently impress ringing current at theclosed ringing key contact 31, the path for this intermittent ringingcurrent being traced from the generator 35, through the circuit breaker59, ringing key contact 31, conductor 61, closed front contact 60 of theflip flop relay 54, the closed front contact of supervisory relay 24,conductor 22, tip contacts of the plug and jack, the limbs of thetelephone line and the substation ringing apparatus, sleeve contacts ofthe plug and jack, the sleeve strand 62 of the cord circuit, contact 51.of the flip flop relay 46, non-inductive resistance 63 to ground throughbattery 12. The non-inductive resistance 63 is provided to prevent theringing current from flowing through the sleeve supervisory relay 24from the point 64, and passing to ground through conductor 42 andbattery 6, thus chattering said relay. This intermittent ringing currentcontinues until the sub scriber removes his receiver from the hook whichcloses a path for battery current through the substation apparatusoperating the tip supervisory relay 41 and opening the locking circuitof control relay 46 by removing the ground 44 therefrom. The ringingcurrent therefore continues until the subscriber responds, when it isautomatically shut off by the removal of his telephone from the hookwhich closes a path for current through the supervisory relay 41, thusrestoring the ringing apparatus to normal condition. This current flowthrough the substation apparatus may be traced from battery 6 throughconductors 42 and 65, the winding of supervisory relay through thenon-inductive resistance 63,

and armature 52 opening the locking circuit of the control relay 16. Thecircuit of the flip-flop relay 54; is interrupted at contact 52 of thecontrol relay 4:6 and also at the contact etet of supervisory relay e1.The response of the called subscriber therefore restores all parts ofthe ringing apparatus to normal condition. The energization ofsupervisory relay 4:1 also removes the ground from the circuit ofsupervisory lamp 39, extinguishing the lamp and indicating to theoperator that the subscriber has responded to the call.

At the termination of the conversation, either subscriber by replacinghis telephone upon the hook, opens the circuit through the supervisoryrelay 17 or 41, thus lighting the corresponding supervisory signal 18 or39 to indicate this fact to the operator. The ringing circuit however,is not established by the restoration of the ground 14 due to thedeenergization of tip supervisory relay 4C1, due'to the fact that thecircuit of the flip-flop relay is open at contact 52 of the controlrelay 16, and the circuit of control relay 16 is open at this point, andalso at the key contacts 1-5. Upon seeing the supervisory lamps lighted,the operator removes the plug from the jacks, restoring all parts of thesystem to normal condition.

In Fig. 2 I have shown a trunk circuit equipped with my ringingarrangement for signaling subscribers where the call originates at adistant office. The ringing arrangement may be used with various formsof trunk circuits and I do not wish to be limited to the form shown.Assuming the subscriber on line A, Fig. 1 desires a connection with asubscriber whose line terminates at a distant exchange, the cord circuitshown in Fig. 1 would be used at the first exchange, and the trunkcircuit shown in Fig. 2 would be used for completing the connection withthe subscriber at the distant exchange, the calling plug of the cordcircuit in Fig. 1 be ing inserted in the jack of the trunk circuit inFig. 2 instead of being inserted directly into the jack of the desiredline.

The operation of the system in making a connection with the trunkcircuit as above described would be as follows: The operator at theoflice where the call originated would notify the operator at thedistant office by means of order wire 66 connected with her headtelephone, the number of the subscriber desired, and the operator at thedistant exchange would reply telling the first operator the number ofthe trunk circuit to be used in making the connection. The firstoperator would then insert the calling plug of the cord circuit into thejack 67 of the trunk circuit designated. An im pedance coil 68 is leggedto ground from the sleeve side of the trunk circuit, through which thesupervisory calling relay 24; of the cord circuit would be energized toclose the circuit of the supervisory cord signal 39, the impedance coil68 performing the same function in this respect as the cut-off relay 35when the cord circuit is inserted directly into the jack of the desiredline. lVhen the calling plug of the cord circuit is inserted in the jack67 of the trunk, a path for current is closed from battery 6, throughconductors Q2 and 65, supervisory relay 2%, sleeve strand of the cordcircuit 62, sleeve contacts of the plug and jack, trunk conductor 112and 69, the winding of high resistance relay 70, conductor 71, tipcontacts of the jack and plug, conductors 22 and 66, and the winding ofthe tip supervisoryrelay ll to ground. The resistance of the trunk relay70 is such that the tip cord relay 11 is not energized in response tothis flow of current so that its armature is not attracted, and thesupervisory lamp 39 continues to glow to indicate to the operator at thefirst exchange that the connection has not yet been completed with thedesired subscriber. The high resistance relay 70 is energized inresponse to this flow of current, attracting its contact 72 and closinga circuit through the guard and disconnect lamp 73, which may be tracedfrom battery 74, through conductors 75 and 76 and to ground through thenormally closed back contact 77 of sleeve supervisory relay 78. If thefirst operator therefore connects with the trunk circuit before thesecond operator plugs into the desired line, the guard lamp 73 will belighted over the above path, or if the first operator should plug intothe wrong trunk through mistake and the second operator should plug intothe desired line, thus energizing the sleeve supervisory relay 78, theguard lamp 73 would be energized over a path traced from battery 7t,through conductor 75, normally closed contact 72 of the highresistance-relay 70, conductor 79, normally closed contact of tipsupervisory relay 80, conductors 81 and S2 to ground through the closedfrontcontact 77 of the sleeve supervisory relay 7 8. After the operatorat the first exchange has plugged into the correct trunk and theoperator at the second exchange has plugged nal of a busy line.

into the desired line, the guard lamp 73 would be extinguished, thefirst circuit traced for it being opened in that event at the normallyclosed contact 77 of super visory relay 78, and the second circuittraced for it being opened in that event at contact 72 of the highresistance relay 70.

The testing apparatus for determining the idle or busy condition of thedesired line is the same with the trunk circuit shown as in the cordcircuit of Fig. 1, the test being obtained by means of the impedancecoil 83 connected normally between the tip of the plug and ground, andadapted to discharge through the tertiary winding of the operatorsinduction coil when the tip of the plug is touched to and removed fromthe termi- Assuming the second operator finds the desired line to beidle, she inserts the plug of the trunk in the jack of the line,energizing the sleeve supervisory relay 78 from battery 74, overconductor 84, the winding of said relay and the sleeve strand of thetrunk circuit to ground, through the cut-oil relay of the desired line.The energization of the supervisory relay 78 closes a path for currentthrough ring lamp 85, from battery 74, through conductor 86, normallyclosed contacts of relay 87, conductor 82, and the contacts ofsupervisory relay 78 to ground. The ring lamp 85 will therefore remainlighted until the subscriber responds to the call.

After inserting the plug in the jack of the desired line, the operatorwill throw her ringing key which will connect the generator 88intermittently through the circuit breaker 89 with the front contact ofthe flip-flop relay 90, through conductor 91. The flip-flop relay willbe energized to extend this ringing current over the line by theactuation of the ringing key contact 92, this circuit through thefiip-fiop relay being traced from battery 74 through the circuit breaker93, flip-flop relay 90, conductor 94, ringing key contact 92, conductors95, and. 79, normally closed contacts of relay 80 and conductors 81 and82 through the closed contact 77 of supervisory relay 78. The operationof the key 92 also closes a path for current through the control relay96 which may be traced from battery 74, conductor 97, coil of saidrelay, conductors 98 and 94, contact92, conductors 95 and 79, normallyclosed contacts of relay 80, and conductors 81 and 82 to ground throughcontact 77 of supervisory relay 78. The attraction of contact spring 99of control relay 96 closes a locking circuit for" said relay frombattery 74 through conductor 97, the winding of said relay, closedcontact 99, conductors 100 and 79, closed contacts of relay 80 andconductors 81 and 82 to ground through contact 77 of relay 78. Theactuation of control relay 96 also opens the trunk circuit at contacts101 and 102 of said relay to prevent the ringing current from going backover the line to the calling subscriber. A non-inductive resistance 103is employed to provide a shunt about the supervisory relay 78 for theringing current. The calling plug of the cord circuit is now inserted inthe jack 67 of the trunk and the supervisory cord lamp 39 is lighted dueto the high resistance of the trunk relay which prevents the cordsupervisory relay 41 from being actuated, and the calling plug of thetrunk circuit is inserted in the jack of the desired line, lighting thering lamp 85 through the contacts of the supervisory relay 78. In thiscondition the intermittent ringing current is being sent over the linefrom generator 88 which may be traced from said generator through thecircuit breaker 89, contacts of the ringing key, conductor 91, thevibrating contact of flip-flop relay 90, conductor 104, front contact ofsupervisory relay 78, conductor 105, over the telephone line and throughthe substation ringing apparatus, sleeve strand 106 of the trunkcircuit, contact 102 of control relay 96, non-inductive resistance 103,and conductor 97 to ground through battery 74. Said ringing current isprevented from flowing through the supervisory relay 78 chattering saidrelay by the shunt circuit containing the non-inductive resistance 103.'When the subscriber responds to this ringing current a path for currentis completed through the substation apparatus and through supervisoryrelay 80 which may be traced from battery 74, conductor 84, supervisoryrelay 78, sleeve strand 106, the telephone line, conductors 105, 104 and107 through the winding of supervisory relay 80 to ground. Thesupervisory relay 80 is energized by current in this path and attractsits armature 108 which removes the ground 77 from the look ing circuitof control relay 96, deenergizing said relay and permitting it torelease 1ts contacts. The denergization of control relay 96 completesthe trunk circuit for conversation at its contacts 101 and 102. Thisalso opens the circuit of the flip-flop relay 90 restoring the ringingapparatus to normal.

The attraction of contact spring 108 of supervisory relay 80 closes apath for current through relay 87 which may be traced from battery 74,through the winding of said relay, conductor 109, contact 108, andconductors 81 and 82 to ground through contact 77 of supervisory relay 78. The operation of relay 87 opens the circuit of ringing lamp 85, thusindicating to the operator that the called subscriber has responded, anda locking circuit is established for said relay 87 from battery 74through the winding of said relay, its front contact 110 and conductor82 to ground through contact 77 of relay 78. This locking circuitprevents the lamp 85 from being re-lighted when the calling subscriberrestores his telephone at the completion of the conversation. Theoperation of supervisory relay 80 when the called subscriber respondsalso operates to open the circuit of high resistance relay 70. This isdue to the attraction of contact 111 of supervisory relay 80. Theattraction of armature 111 of relay 8() also closes a path ofcomparatively low resistance through supervisory relay 41 at the firstexchange. Supervisory relay 41 is responsive to this flow of current,attracting its armature and extinguishing the supervisory lamp 39, thusnotifying the operator at the first exchange that the called subscriberhas responded. The flow of current through supervisory relay 41 may betraced from battery 6 through conductors 42 and 65, supervisory relay24, sleeve cord strand 62, the sleeve contacts of the plug and jack,trunk strand 112, repeat ing coil winding 113, front contact 111 ofrelay 80, trunk strand 114, tip contacts of the plug and jack,conductors 22 and 66 through the winding of tip supervisory relay 41 toground.

It will be seen that the supervision of the connection is performedentirely by the operator at the first exchange. The guard lamp 73 isprevented from lighting when the subscriber replaces his telephone uponthe hook, its circuit being open at contact 108 of supervisory relay 80when the high resistance relays is deenergized, and its circuit beingopen at contact 77 of supervisory relay 78 when the high resistancerelay 70 is actuated. Similarly, the circuit of ringing lamp 85 isopened at contact 110 of relay 87, regardless of whether the subsscribers telephone is on or off the hook. hen the subscribed replaceshis telephone upon the hook, supervisory relay 80 is deenergized, itsarmature 111 drops back again, inserting the high resistance relay 70 inthe circuit in series with supervisory cord relay 41. Due to the highresistance of relay 70, cord supervisory relay 41 does not obtainsufficient current to maintain it actuated, its armature 44 drops backclosing the circuit of supervisory lamp 39, which is lighted to informthe operator at the first exchange that the called subscriber hasterminated the conversation. The operator then removes the plug from thetrunk circuit deenergizing the high resistance relay 70 and closing apath for current for the lamp 7 3 from battery 74, over conductor 75,contact 72 of high resistance relay 70, conductor 79, closed backcontact 108 of supervisory relay 80 and conductors 81 and 82 to groundthrough contact 77 of supervisory relay 78. Upon seeing the operation ofdisconnect lamp 73, the operator at the second exchange would know thatthe first operator had taken down the connection and would remove theplug from the ack of the subscribers line restoring all apparatus tonormal condition.

It should be understood that the ringing system and apparatus is thesame in Fig. 2 as that shown in Fig. 1 and is intended to be operated inthe same manner, being adapted for use with a trunk circuit instead ofwith an operators cord circuit.

Vhile I have described my invention with reference to the details ofconstruction, it is to be understood that many changes may be made inthe apparatus and arrangements shown without depart-ing from the spiritor scope of the invention and for this reason I do not wish to belimited to the arrangement shown, but intend to cover modifications ofthe invent-ion that realize the advantages and benefits thereof.

I claim:

1. A telephone system comprising a calling and a called line, anoperators link circuit uniting said lines, a ringing key, normally opencontacts therefor, a control relay, an initial energizing circuit forsaid relay closed responsive to actuation of said key and contacts, asupervisory relay, a locking circuit for said control relay includingcontacts of said supervisory relay and effective upon energization ofsaid control relay, a flip-flop relay operated responsive to theenergization of said control relay, the energizing circuit of saidflipflop relay also including contacts of said supervisory relay.

2. In a telephone system, the combination with a called subscriberstelephone line, of an operators link circuit connected thereto, aringing key, a control relay, means for energizing said relay responsiveto as tuation of said key, talking strands of said link circuitdisunited upon energization of said control relay, a supervisory relay,a source of ringing current, a flip-flop relay operated responsive tothe energization of said control relay, the energizing circuit of saidflip-flop relay being jointly controlled through contacts on saidcontrol and supervisory relays, the said flip-flop relay in itsoperation alternately bridging said ringing source and supervisory relayacross the called line, and means controlled by the called subscriber toenergize said supervisory relay, whereby said control relay isdeenergized to restore the continuity of the link circuit strands, andsaid flip-flop relay is rendered inoperative.

3. In a telephone system, the combination with a calling and a calledtelephone line, of a link circuit establishing connection between saidline, an operators ringing key actuated to call the desired subscriber,a control relay energized responsive to said actuation to disunite thetwo lines, a supervisory relay, a flip-flop relay, alocking circuit forsaid control relay and an energizing circuit for said flip-flop relayefiective upon energization of said control relay, said circuitsincluding contacts of said supervisory relay, said supervisory re-' toclose an initial energizing circuit for said control relay whereby saidflip flop relay is operated to connect said ringing current with thecalled line, a tip supervisory relay, a substitute locking circuit forsaid c011- trol relay effective upon its actuation including normalcontacts of the tip relay, and means controlled at the substation forenergizing said tip relay to cause the restor ation of said control andflip flop relays whereby said ringing current is disconnected.

Signed by me at Chicago, county of Cook, and State of Illinois, in thepresence of two Witnesses.

ALFRED H. WEISS. l/Vitnesses:

,MARJORIE E. GRIER,

WM. BERGHAHN.

(iopies of this patent may be obtained for five cents each, byaddressing the Commissioner of Patents, Washington, D. G.

